In order to accurately analyze and evaluate the output beam quality of large-aperture laser amplifiers, we established a new method of simulating thermal effects which can analyze the distributed thermal effects in the direction of optical transmission. In this method, gain medium would be divided to several segments. Thermal effects and beam propagation in every segment are calculated and cascaded to the next one in the direction of optical transmission until the end of gain medium rod. To achieve propagation of aperture-level distance in these segments, a close-range propagation algorithm based on angular spectrum is proposed and its correctness is verified by comparing with theoretical results obtained by Fresnel diffraction. Though this new method, simulations of the thermal effects in simplified amplifiers with two gain medium rods that compensate each other at different apertures were carried out. The results show that residuals of depolarization loss increase with aperture. When the diameter is up to 35mm, the maximum depolarization loss is 98.8%. This new method of simulating thermal effects lays a solid foundation for the further research on large-aperture highrepetition- rate laser systems.
A preliminary concept design of a diode pump solid-state Nd: glass laser amplifier based on helium-cooled multi-slab geometry is presented. The laser amplifier is designed to obtain an output of 100 J/10 Hz. The gain slabs applied in the laser amplifier can lead to low thermally induced wavefront distortion, which are based on heating the edge by the cladding layer. In addition, we also develop a comprehensive numerical model for study effect of amplifier spontaneous emission on the stored energy and thermo-optic effects in the Nd: glass laser amplifier. The results of simulations show that energy storage efficiency of 48% and the average volume density of the stored energy greater than 0.55 J/cm3 are obtained for the laser amplifier. The wavefront distortion can be decreased to 0.78 λ for a gain slab in the laser amplifier.
We demonstrated a broadband Nd: glass laser amplifier with controllable gain bandwidth in experiment, which is expected to be used in high energy low coherent laser amplifier system. A birefringent crystal for spectral filtering in regenerative laser amplifier was designed and proposed, and the parameters of birefringent crystal was optimized in simulation. The birefringent crystals with different bandwidths were designed by this method. The laser amplification output with different gain bandwidths of 6~10 nm was realized, which was also verified by experiments. This broadband Nd: glass laser amplifier is expected to be used in large scale broadband laser amplification system, and provides important technical support for a new type of broadband tunable nanosecond high-power laser facility.
We demonstrated the arbitrary pulse shaping for a high power, joules class, and multi-pass ring Nd: glass laser amplifier system with nanosecond pulses based on the direct calculation method. While the square pulse with pulse energy 0.9mj and FWHM (full width at half maximum) pulse width 6ns, a 0.9J at 1Hz high power laser pulse energy is generated, which has the ability to change the waveform arbitrarily based on the full fiber front end. The laser amplifier system consists of three parts: full fiber seeder, diode pumped Nd: glass regenerative amplifier, and multi-pass ring amplifier. With the help of direct calculation method based on the input-output model, the input pulse shape has been calculated and the output pulse shape has been compared to the target pulse shape, showing that the simulation and experiment is consistent. Some other interesting pulse shapes have been produced with pre-compensated inject pulse based on the calculation which shows great potential to be applied in high power laser amplifier system with a desired pulse shape.
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